The present invention relates to an active energy beam-curable adhesive composition capable of bonding various base materials by irradiation with active energy beams such as electron beams and ultraviolet rays. The composition of the present invention is preferably used for bonding thin layer adherends such as plastic films or plastic sheets. Further, it is preferably used for manufacturing various optical films or sheets to be used in liquid crystal display elements and the like. Thus, it can advantageously be used in these technical fields.
Conventionally, in a laminating method in which bonding is achieved between thin layer adherends such as plastic films or sheets, or between a thin layer adherend such as a plastic film or sheet and another thin layer adherend made from a different material, there has been principally employed a dry laminating method in which a solvent type adhesive composition including an ethylene-vinyl acetate copolymer or a polyurethane polymer is coated on a first thin layer adherend, and dried, and a second thin layer adherend is then compression bonded thereto by means of a nip roller or the like.
The adhesive composition used in this method generally contains a large amount of solvent for uniforming the coated amount of the composition. For this reason, the solvent evaporates in large amounts during drying, presenting the problems of toxicity, working safety and environmental pollution. Further, the adhesive composition also causes a problem that peeling occurs between thin film adherends in a post-processing step conducted immediately after bonding the thin layer adherends together, such as in a heat sealing step for ensuring the bonding of the resulting laminated film, and in a ruling step for engraving grooves.
A solventless adhesive composition has been examined as an adhesive composition for solving these problems.
As a solventless adhesive composition, a two-part adhesive composition or an adhesive composition curable by active energy beams such as ultraviolet rays and electron beams has been widely used.
As a two-part adhesive composition, there has been prevalently used a so-called polyurethane adhesive composition including a polymer having a hydroxyl group at the terminal as a base agent, and a polyisocyanate compound having an isocyanate group at the terminal as a curing agent. However, the composition has a deficiency that too much time is required for curing. For this reason, there have occurred problems in terms of production such that the post-processing steps such as a ruling step cannot be started immediately after bonding the thin layer adherends.
In contrast, the active energy beam-curable adhesive composition is excellent in productivity because of its high curing speed, and hence has received attention in recent years.
On the other hand, liquid crystal display apparatuses have been widely used as display devices such as compact televisions, portable personal computers, portable telephones, and word processors, including simple display apparatuses in digital watches and various electric appliances as a matter of course. In recent years, the active energy beam-curable adhesive has also come into use in bonding of various optical films used in the liquid crystal display devices.
The adhesive composition to be used in the optical film has been required to have such a performance as to be capable of holding its adhesive force under extreme conditions of high temperatures and high humidities.
However, while most of conventional active energy beam-curable adhesives have been excellent in initial adhesive strength, they may show a reduction in adhesive strength after long-duration use under high temperature or high humidity conditions, resulting in peeling, or whitening due to moisture absorption.
The present inventors have already proposed a composition including urethane (meth)acrylate and imide (meth)acrylate with a specific structure as a composition applicable for various uses, including use as an adhesive (Japanese Laid-Open (Kokai) Patent Publication No. Hei 10-36462).
The composition has been more excellent in adhesion under high temperature and high humidity conditions as compared with conventional active energy beam-curable adhesive composition when used as an adhesive for manufacturing an optical film, but has not reached the practical level.
In view of the foregoing problems, the present inventors have intensively studied and it is therefore an object of the present invention to provide an active energy beam-curable adhesive composition excellent in adhesion under high temperature and high humidity conditions, and at a practicable level.
As a result of various studies, the present inventors have found that an active energy beam-curable adhesive composition which comprises a specific urethane (meth)acrylate and a compound having a specific cyclic imide group is excellent in adhesion under either condition of high temperature or high humidity and at a practicable level, and have completed the present invention.
Below, the present invention will be described in details.
It is noted that, in this specification, acrylate and/or methacrylate is referred to as (meth)acrylate, an acryloyl group and/or a methacryloyl group is referred to as a (meth)acryloyl group, and acrylic acid and/or methacrylic acid is referred to as (meth)acrylic acid.
1. (A) Urethane (meth)acrylate Derived from Polyester Polyol or Polycarbonate Polyol
The component (A) in the present invention is urethane (meth)acrylate derived from polyester polyol or polycarbonate polyol. The urethane (meth)acrylate provides a particularly excellent adhesive strength under high humidities.
As the component (A), both of the oligomer and polymer are usable, and the one having a weight-average molecular weight of 500 to 30,000 is preferred. It is noted in the present invention that the weight-average molecular weight is defined as a polystyrene-converted value of the molecular weight determined by gel permeation chromatography.
Examples of urethane (meth)acrylate include a compound obtained by allowing the reaction product of polyester polyol or polycarbonate polyol and organic polyisocyanate to react with (meth)acrylate containing hydroxyl group.
Examples of polycarbonate polyol include the reaction product between low molecular weight polyol (described later), polyether polyol (described later) and/or bisphenol such as bisphenol A, and ethylene carbonate and carboxylic acid dialkyl ester such as carboxylic acid dibutyl ester. Examples of polyester polyol include the esterification reaction product between low molecular weight polyol (described later) and/or polyether polyol (described later) and each acid component of dibasic acid such as adipic acid, succinic acid, phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, or terephtalic acid, or anhydrides thereof.
Here, examples of the low molecular weight polyol include ethylene glycol, propylene glycol, 1,6-hexanediol, cyclohexane dimethanol, and 3-methyl-1,5-pentanediol. Examples of polyether polyol include polyalkylene glycols such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol, and diol of a block or randompolymer such as polyethylene polypropoxy block polymer diol.
Examples of the organic polyisocyanate include tolylene diisocyanate, 1,6-hexane diisocyanate, 4,4xe2x80x2-diphenylmethane diisocyanate, polymethylene polyphenylisocyanate, 1,6-hexane diisocyanate trimer, hydrogenated tolylene diisocyanate, hydrogenated 4,4xe2x80x2-diphenylmethane diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, paraphenylene diisocyanate, tolylene diisocyanate dimer, 1,5-naphthalene diisocyanate, hexamethylene diisocyanate adduct, 4,4xe2x80x2-dicyclohexylmethane diisocyanate, trimethylolpropane tris(tolylene diisocyanate) adduct, and isophorone diisocyanate.
Examples of the hydroxyl group-containing (meth)acrylate include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxypentyl (meth)acrylate, hydroxyhexyl (meth)acrylate, hydroxyoctyl (meth)acrylate, pentaerythritol tri-, di-, or mono(meth)acrylate, and trimethylolpropane di- or mono(meth)acrylate.
These are obtained in the following manner. Namely, in the presence of an addition catalyst such as dibutyltin dilaurate, an organic isocyanate and a polyol component are heated under agitation to undergo an addition reaction. Further, hydroxyalkyl (meth)acrylate is added thereto to be heated under agitation, effecting the addition reaction.
In the present invention, if required, urethane poly(meth)acrylate other than those mentioned above can also be used in combination. Examples thereof include the compounds described on pages 70 to 74 of the xe2x80x9cUV/EB Curable Materialxe2x80x9d published in 1992 by CMC Co., Ltd.
2. (B) Compound Having at Least One Ethylenically Unsaturated Group Together with at Least One Cyclic Imide Group
The component (B) is a compound having at least one ethylenically unsaturated group together with at least one cyclic imide group represented by the following general formula (1): 
(where R1 and R2 are each independently a hydrogen atom or an alkyl group having 4 or less carbon atoms, or R1 and R2 represent an unsaturated or saturated hydrocarbon group of a 5- or 6-membered ring formed by linkage with each other.)
In the above formula (1), it is preferable that at least one of R1 and R2 is the alkyl group having 4 or less carbon atoms, and it is also preferable that R1 and R2 are the unsaturated or saturated hydrocarbon group of a 5- or 6-membered ring formed by linkage with each other. Specific examples thereof include xe2x80x94CH2CH2CH2xe2x80x94, xe2x80x94CHxe2x95x90CHCH2xe2x80x94, xe2x80x94CH2CH2CH2CH2xe2x80x94, xe2x80x94CH2CHxe2x95x90CHCH2xe2x80x94, or xe2x80x94CHxe2x95x90CHCHxe2x95x90CHxe2x80x94 group.
As the component (B), the imide (meth)acrylate represented by the following general formula (2) is preferred in terms of ease of its manufacturing: 
(where R1 and R2 are each independently a hydrogen atom or an alkyl group having 4 or less carbon atoms, or R1 and R2 represent an unsaturated or saturated hydrocarbon group of a 5- or 6-membered ring formed by linkage with each other; R3 represents a straight-chain or branched alkylene group having 1 to 6 carbon atoms; R4 represents a hydrogen atom or a methyl group; and n denotes an integer of 1 to 6.)
Out of the compounds represented by the general formula (2), the compounds represented by the following general formulae (3) to (5) are more preferred. 
(where R4 and R5 each represents a hydrogen atom or a methyl group, and n denotes an integer of 1 to 6.) 
(where R4 and R5 each represents a hydrogen atom or a methyl group, and n denotes an integer of 1 to 6.) 
(where R4 and R5 each represents a hydrogen atom or a methyl group, and n denotes an integer of 1 to 6.)
The compound represented by the general formula (2) can be manufactured from an acid anhydride, amino alcohol, and unsaturated carboxylic acid by the methods described in the following documents including patent publications:
Kiyoshi Kato, et al., xe2x80x9cJournal of Synthetic Organic Chemistryxe2x80x9d 30(10), 897, (1972);
Javier de Abajo et al., xe2x80x9cPolymerxe2x80x9d, vol. 33(5), (1992); and
Japanese Laid-Open (Kokai) Patent Publication No.Sho 56-53119, and Japanese Laid-Open (Kokai) Patent Publication No.Hei 1-242569.
3. (C) Compound Having at Least One Ethylenically Unsaturated Group
To the composition of the present invention, there can be added, if required, a compound having at least one ethylenically unsaturated group.
As the component (C), various compounds can be used so long as they are not the compounds (A) and (B). Examples of the component (C) include monomers, oligomers, and polymers.
The components (C) can be used in combination of two or more thereof.
3-1. Monomer
As the monomer, there can be mentioned a compound having one (meth)acryloyl group. Examples of the compound include ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.
Further, in addition to (meth)acrylates, mention may be made of (meth)acrylamide derivatives such as N-methyl acrylamide, N-isopropyl acrylamide, N,N-dimethylaminopropyl acrylamide, N,N-dimethyl acrylamide, N-vinyl formamide, N-vinyl-N-methyl formamide, N-vinylacetoamide, N-vinyl-N-methylacetoamide, and acryloylmorpholine; and N-vinyl compounds such as N-vinylpyrrolidone and N-vinylcaprolactam.
Examples of a compound having two or more (meth)acryloyl groups include alkylene glycol di(meth)acrylates such as ethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, and tripropylene glycol di(meth)acrylate; glycol di(meth)acrylates such as 1,6-hexanediol di(meth)acrylate and neopentyl glycol di(meth)acrylate; bisphenol type di(meth)acrylates such as bisphenol A di(meth)acrylate or halogen-nucleus-substituted products thereof, and bisphenol F di(meth)acrylate or halogen-nucleus-substituted products thereof; polyol poly(meth)acrylates such as dimethylol tricyclodecane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol hexa(meth)acrylate; poly(meth)acrylates of alkylene oxide adducts of the polyols; and di-, or tri(meth)acrylates of isocyanuric acid alkylene oxide.
In addition to these compounds, there can be mentioned the compounds as described on pages 53 to 56 of xe2x80x9cThe Latest UV-Curable Technologyxe2x80x9d published in 1991 by Printing Information Association Co., Ltd., and the like.
3-2. Oligomer
Examples of oligomer include polyester (meth)acrylate, epoxy (meth)acrylate, and polyether (meth)acrylate.
3-2-1. Polyester (meth)acrylate Oligomer
Examples of polyester (meth)acrylate oligomer include dehydrated condensates of polyester polyol and (meth)acrylic acid.
Here, as polyester polyol, there may be mentioned the reaction products of polyol, and carboxylic acid or anhydride thereof. Examples of polyol include low molecular weight polyols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, butylene glycol, polybutylene glycol, hexamethylene glycol, neopentyl glycol, cyclohexane dimethanol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, trimethylolpropane, glycerin, pentaerythritol, and dipentaerythritol, and alkylene oxide adducts thereof. Examples of carboxylic acid or anhydride thereof include dibasic acids such as orthophthalic acid, isophthalic acid, terephthalic acid, adipic acid, succinic acid, fumaric acid, maleic acid, hexahydrophthalic acid, tetrahydrophthalic acid, and trimellitic acid, and anhydrides thereof.
As polyester poly(meth)acrylates other than these compounds, there can be mentioned the compounds as described on pages 74 to 76 of the aforesaid literature xe2x80x9cUV/EB-Curable Materialxe2x80x9d, and the like.
3-2-2. Epoxy (meth)acrylate Oligomer
Epoxy (meth)acrylate is a compound obtained from the addition reaction of epoxy resin and (meth)acrylic acid. Examples thereof include the compounds as described on pages 74 to 75 of the aforesaid literature xe2x80x9cUV/EB-Curable Materialxe2x80x9d, and the like.
Examples of epoxy resin include aromatic epoxy resins and aliphatic epoxy resins.
Specific examples of aromatic epoxy resins include resorcinol diglycidyl ether; di-, or polyglycidyl ethers of bisphenol A, bisphenol F, bisphenol S, bisphenol fluorene, or alkylene oxide adducts thereof; novolac epoxy resins such as phenolic novolac epoxy resins and cresol novolac epoxy resins; glycidyl phthalimide; and o-phthalic acid diglycidyl ester. In addition to these compounds, there can be mentioned the compounds as described in chapter 2 of xe2x80x9cEpoxy Resin-Recent Advance-xe2x80x9d published in 1990 by Shokoudo, and on pages 4 to 6 and 9 to 16 of xe2x80x9cPolymer Processingxe2x80x9d extra issue 9 of vol.22 on epoxy resins (published in 1973 by Polymer Publication Society).
Specific examples of aliphatic epoxy resins include diglycidyl ethers of alkylene glycols such as ethylene glycol, propylene glycol, 1,4-butanediol, and 1,6-hexanediol; diglycidyl ether of polyalkylene glycol such as polyethylene glycol and polypropylene glycol; diglycidyl ethers of neopentyl glycol, dibromoneopenyl glycol, and alkylene oxide adducts thereof; polyglycidyl ethers of polyhydric alcohols such as di-, or triglycidyl ethers of trimethylolethane, trimethylolpropane, glycerin, and alkylene oxide adducts thereof, and di-, tri-, or tetraglycidyl ethers of pentaerythritol and alkylene oxide adducts thereof; di-, or polyglycidyl ethers of hydrogenated bisphenol A and alkylene oxide adducts thereof; tetrahydrophthalic acid diglycidyl ether; and hydroquinone diglycidyl ether. In addition to these compounds, there can be mentioned the compounds described on pages 3 to 6 of the aforesaid literature xe2x80x9cPolymer Processingxe2x80x9d extra issue on epoxy resin.
Other than these aromatic epoxy resins and aliphatic epoxy resins, there can be mentioned an epoxy compound having a triazine nucleus in the structure, such as TEPIC (trade name: Nissan Chemical Industries Co., Ltd.), or Denacol EX-310 (trade name: Nagase Kasei Co., Ltd.) Further, there can also be mentioned the compounds as described on pages 289 to 296 of the aforesaid literature xe2x80x9cPolymer Processingxe2x80x9d extra issue on epoxy resin.
In the foregoing compounds, the alkylene oxides for use in alkylene oxide adducts are preferably ethylene oxide, propylene oxide, and the like.
3-2-3. Polyether (meth)acrylate Oligomer
Examples of polyether (meth)acrylate oligomer include polyalkylene glycol di(meth)acrylates such as polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate.
3-3. Polymer
As the polymer, there can be mentioned (meth)acrylic polymers having (meth)acryloyloxy groups and those obtained by introducing (meth)acryloyl groups into the side chains of a (meth)acrylic polymer having functional groups, e.g., the compounds as described on pages 78 to 79 of the aforesaid literature xe2x80x9cUV/EB Curing Materialxe2x80x9d.
4. Mixing Ratio
In the present invention, the ratio of the components (A), (B), and (C) is preferably the component (A) 5 to 50% by weight; the component (B) 10 to 95% by weight; and the component (C) 0 to 85% by weight.
When the ratio of the component (A) is less than 5% by weight, the adhesive force under high temperatures on the adherend may be reduced. On the other hand, when it is more than 50% by weight, the initial adhesive force or the adhesive force under high humidities on the adherend may be reduced.
When the ratio of the component (B) is less than 10% by weight, the adhesive strength under high temperatures or high humidities on the adherend may be reduced. On the other hand, when it is more than 95% by weight, the adhesive strength under high temperatures on the adherend may be reduced.
When the ratio of the component (C) is more than 85% by weight, the initial adhesive force and the adhesive force under high temperatures or high humidities on the adherend may be reduced.
5. Other Components
When the composition of the present invention is cured by ultraviolet rays, if required, a photopolymerization initiator may also be mixed therein.
Examples of the photopolymerization initiator include benzonins and alkyl ethers thereof such as benzoin, benzoin methyl ether, benzoin ethyl ether, and benzoin isopropyl ether; acetophenones such as acetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 1,1-dichloroacetophenone, 1-hydroxyacetophenone, 1-hydroxycyclohexyl phenyl ketone, and 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propane-1-one; anthraquinones such as 2-methylanthraquinone, 2-ethylanthraquinone, 2-tertiary-butylanthraquinone, 1-chloroanthraquinone, and 2-amylanthraquinone; thioxanthones such as 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthone, and 2,4-diisopropylthioxanthone; ketals such as acetophenone dimethyl ketal and benzyldimethyl ketal; monoacylphosphine oxide such as 2,4,6-trimethylbenzoyl diphenylphosphine oxide or bisacylphosphine oxide; benzophenones such as benzophenone; and xanthones.
These photopolymerization initialtors can be used alone, or in combination with a photopolymerization promotor of the type of benzoic acid, amine, or the like.
The mixing ratio of the photopolymerization initiator is preferably between 0.1 part by weight and 10 parts by weight, both inclusive, and more preferably between 1 part by weight and 8 parts by weight, both inclusive, per 100 parts by weight of the composition.
Further, in the composition of the present invention, here can be mixed inactive components such as inorganic fillers, softening agents, oxidation inhibitors, antioxidants, stabilizers, tackifying resins , levelling agents, antifoaming agents, plasticizers, dyes, pigments, treating agents, and ultraviolet light screening agents in an amount of up to 100 parts by weight per 100 parts by weight of the total of the components (A), (B), and if required (C). Examples of the tackifying resins include rosins such as rosinic acid, polymeric rosinic acid, and rosinic acid ester, terpene resins, terpene phenol resins, aromatic hydrocarbon resins, aliphatic saturated hydrocarbon resins, and petroleum resins.
6. Manufacturing and Use Methods
The method for manufacturing the composition of the present invention has no particular restriction. The composition can be obtained by stirring or mixing the essential components of the present invention, and if required other components by a conventional method.
The adhesive composition of the present invention can be used for bonding of various base materials. Examples of the base material include plastics, paper, and metals.
The composition may be used in accordance with a commonly used method. There are included a method in which the composition is irradiated with active energy beams after being coated on the base material, and the like.
Examples of the active energy beams include ultraviolet rays, X rays, and electron beams. Out of these, ultraviolet rays are preferred because of the availability of an inexpensive apparatus. As a light source for curing with ultraviolet rays, various ones can be used. For example, there may be mentioned a pressurized or high pressure mercury lamp, a metal halide lamp, a xenon lamp, an electrodeless discharge lamp, and a carbon arc lamp. As an EB irradiation apparatus for curing by electron beams, various apparatuses can be used. Examples thereof include Cockroft-Walton type, van de Graaff type, and resonance type apparatuses, and the energy beams have an energy in a range of preferably 50 to 1000 eV, and more preferably 100 to 300 eV.
The adhesive composition of the present invention is preferably used for bonding sheets of thin layer adherend as base materials.
The adhesive composition may be used for bonding thin layer adherends in accordance with a commonly used method in manufacturing of a laminate. For example, mention may be made of the following method. Namely, the composition is coated on a first thin layer adherend, and if required, dried. Subsequently, a second thin layer adherend is bonded thereto by irradiation with an active energy beam. Here, at least one of the thin layer adherends is required to be a plastic film.
Examples of the thin layer adherend include a plastic film, paper, or metal foil. The plastic film is required to be an active energy beam-transmittable one. The film thickness may be selected according to the thin layer adherend to be used, and the use thereof, but is preferably 0.2 mm or less. Examples of plastics of the plastic film include polyvinyl chloride resin, polyvinylidene chloride, cellulosic resin, polyethylene, polypropylene, polystyrene, ABS resin, polyamide, polyester, polycarbonate, polyurethane, polyvinyl alcohol, ethylene-vinyl acetate copolymer, and chlorinated polypropylene. Examples of the paper include simili paper, woodfree paper, kraft paper, art coated paper, cast coat paper, machine glazed paper, parchment paper, waterproof paper, glassine paper, and corrugated fibreboard. Examples of the metal foil include aluminium foil.
Coating on the thin layer adherend may be accomplished by a conventionally known method. Examples thereof include the methods by means of a natural coater, knife belt coater, floating knife, knife over roll, knife on blanket, spraying, dipping, kiss-roll, squeeze roll, reverse roll, air blade, curtain flow coater, and gravure coater. The thickness of the composition of the present invention to be coated may be selected according to the thin layer adherend to be used and the use thereof, however, it is in a range of preferably 0.1 to 1000 xcexcm, and more preferably 1 to 50 xcexcm.
Since the laminated film or sheet obtained from the adhesive composition of the present invention is excellent in adhesive force under high temperature and high humidity conditions, it can be preferably used as an optical film such as a polarization film and a phase contrast film for use in a liquid crystal display apparatus and the like.